Exoplanets

A New Venus-Sized World Found in the Habitable Zone of its Star

The parade of interesting new exoplanets continues. Today, NASA issued a press release announcing the discovery of a new exoplanet in the Gliese 12 system, sized somewhere between Earth and Venus and inside the host star’s habitable zone. Two papers detail the discovery, but both teams think that the planet is an excellent candidate for follow-up with the James Webb Space Telescope (JWST) to try to tease out whether it has an atmosphere and, if so, what that atmosphere is made of.

But before JWST knew where to look, another workhorse of the exoplanet hunt had to do its job. The Transiting Exoplanet Survey Satellite (TESS) found this planet in a system only 40 light years away. That would make it the closest known example of a rocky, Earth or Venus-sized exoplanet in its star’s habitable zone.

Gliese 12 is a red dwarf, only weighing about 27% of the Sun’s weight. Due to the intricacies of fusion, this amounts to the star outputting about 60% of the light of our Sun, which, in turn, means its habitable zone is much closer than our own. The planet, known as Gliese 12b, orbits its parent star once every 12.8 days. But more importantly, it receives about 85% of the energy that Venus typically receives from the Sun.

Fraser discusses some of the accomplishments of TESS.

The similarity between our closest neighbor and this exoplanet is striking. It could also lead to new discoveries about the formation of our solar system. Current theory holds that Venus and the Earth originally had an atmosphere and then lost it. They diverged to become the Eden-like Earth and the hell-like Venus because of one crucial substance – water.  

Venus’ atmosphere lacked water, so when its current atmosphere started to form, none of the liquid necessary for life as we know it was available. Earth, on the other hand, had plenty of water to spare, allowing it to eventually develop life and humans to evolve there.

One of the holy grails of astrobiology is to find an Earth analog, where the solar radiation, day length, size, atmospheric makeup, and other factors are similar enough for a reasonable chance for life to evolve. We can quickly determine many of those numbers, such as orbit, size, and the amount of solar radiation a planet receives. But finding details like atmospheric makeup is harder.

Artist’s depiction of Gliese 12b in comparison to Earth, with different atmospheres – from no atmosphere at all on the left to a atmosphere like Venus’ on the right.
Credit – NASA / JPL-Caltech/R. Hurt (Caltech/IPC)

Hence why the researchers suggested JWST should get involved. The world’s most powerful space-based telescope would be capable of detecting the atmospheric makeup of Gliese 12b using a technique called transmission spectroscopy. That’s when the light from a planet’s host star is forced through the planet’s atmosphere, and what wavelengths are absorbed can give an astronomer an idea of what kind of gases are present in that atmosphere.

For now, it’s pure speculation whether Gliese12b has any atmosphere. But with some observational time on JWST, scientists should be able to answer that question easily. Until then, workhorses like TESS will keep picking up new exoplanet candidates for JWST to look at. There are undoubtedly some more interesting ones hiding out there amongst the stars—it’s only a matter of time before we find them.

Learn More:
Kuzuhara et al. – Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy
Dholakia et al.- Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS
UT – TESS Finds Eight More Super-Earths
UT – Hubble Succeeds Where TESS Couldn’t: It Measured the Nearest Transiting Earth-Sized Planet

Lead Image:
Artist’s depiction of Gliese 12b and its parent star.
Credit – NASA / JPL-Caltech / R Hurt (Caltech-IPAC)

Andy Tomaswick

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